The properties of ion exchange celluloses have been studied for chromatographic separations and immobilization of enzymes. See, for example, Guthrie et al, Ind. & Eng. Chem., 52, 915-916 (Nov. 1960); Barker et al, Carbohyd. Res., 8, 491-497 (1968); and Wilson et al, Biotech. & Bioeng., XI, 349-361. Natural celluloses modified to incorporate cationic groups, such as tertiary amine or quaternary ammonium groups, are available commercially in microgranular and fibrous forms. The di- and tri-ethylaminoethylated celluloses are referred to, respectively, as DEAE-cellulose and TEAE-cellulose, while the cationic derivative of cellulose prepared by reaction with epichlorohydrin and triethanolamine is known as ECTAEOLA-cellulose. Companies which are understood to have produced cationic celluloses for commercial use include Brown Company, New York, N.Y., W. & R. Balston, Ltd., Kent, England, and Servi Co., Heidelberg, Germany.
As far as is known, however, the only commercial application of enzymes immobilized on an ion exchange cellulose has been in connection with the partial conversion of starch-derived glucose to fructose, thereby obtaining a syrup of increased sweetness. For this purpose, glucose isomerase enzyme is bound to DEAE-cellulose (or similar cationic cellulose), and the glucose syrup is passed through a series of very thin beds of the isomerase-containing cellulose. See, Schnyder, B. J., "Continuous Isomerization of Glucose to Fructose on a Commercial Basis", Die Starke, 26, 409-412 (1974); and Thompson et al U.S. Pat. No. 3,788,945, granted Jan. 29, 1974. This technology, as applied commercially by Standard Brands Incorporated and A. E. Staley & Company, involves the use of contact beds of 1 to 5 inches in thickness. This is necessary so that the pressure drop across each bed is small and the compaction of the bed is minimal. But because of the thinness of the beds, in order to avoid the effects of substrate channeling, it is essential to employ a series of such beds. Consequently, fixed-bed columns, such as are used for processes involving ion-exchange resins, cannot be employed. Instead, pressure leaf filters are used. The glucose isomerase bound to the cellulose carrier is pumped as an aqueous slurry through the pressure leaf filter in such a manner as to cover each leaf evenly with a thin layer of the cellulose material. As disclosed in U.S. Pat. No. 3,788,945, the depth to width ratio of the beds is preferably limited to from about 0.02 to 0.05.
Because of the expense and inconvenience of carrying out glucose isomerization in pressure leaf filters, the corn syrup industry has been actively searching for alternative processes where the glucose isomerase enzyme can be immobilized on a material usable in commercial-size fixed bed columns. Such column materials must effectively immobilize the enzyme; be chemically and physically stable, resisting disintegration under conditions of use; and being sufficiently porous while minimizing channeling effects, so that there is adequate and uniform contacting but with no excessive pressure drop across the bed. Some microorganisms which produce isomerase contain this enzyme in the cell, and the enzyme is bound therein, or can be bound by a heat treatment. For example, a column material can be prepared for Arthrobacter cells. One process is described in U.S. Pat. No. 3,821,086. Such natural column material shows considerable promise, and provides advantages over the use of shallow beds of cellulose-immobilized isomerase. However, the need is great for a column material of general utility, which can be used for immobilizing soluble isomerase, as well as other soluble enzymes, such as those used for the conversion of starch oligosaccharides to dextrose and maltose. Such a column material could be used to immobilize alpha amylase, glucoamylase, or mixtures thereof, for commercial production of corn starch-derived syrups having D.E.'s from 40 to 97.
In particular, to minimize capitol investment, increase plant capacity and reduce production costs, there has been a manifest need for a column process to produce intermediate D.E. corn syrups, such as the syrups now produced by enzymatic hydrolysis of corn starch to obtain syrups having a D.E. in the range of about 40 to 70. As far as is known, all present commercial processes for producing this type of syrup utilize a final stage batch enzyme treatment in which the soluble enzymes are dissolved in the syrup. This is a one-time enzyme use. Usually, the final stage involves treatment simultaneously with an alpha-amylase and a glucoamylase. Therefore it would be desirable to provide a column material to which a mixture of these enzymes can be chemically bonded and immobilized therein. Such a column material and column apparatus would also have many other applications, and could be used, in general, wherever batch enzyme treatments of substrates with soluble enzymes are now used.